Adult krill can reach lengths of up to fifteen centimeters, though most are less than a third that size. They remain fairly small creatures, especially compared to the much larger animals that eat them. As adults, krill are capable of swimming against weak currents. They use this to their advantage to avoid predators during the day, preferring to spend time at depth while diurnal predators are active, and wandering closer to the surface at night. However, strong currents can produce upwells that sweep swarms of krill to the surface of the water where they can incite a feeding frenzy among their usual predators. Some krill can escape these events by diving to lower depths, though they can also shed their exoskeletons to use as a decoy for a hungry predator. Whether they escape or not, hatchmate pairs stick close together to ensure they endure the same fate.

The cold northern and southern oceans are home to many marvelous creatures, but almost all of them depend, in one way or another, on these tiny crustaceans. Krill are the base of the arkenian food chain, at their peak season forming masses that weigh millions of tons. Whales, seals, penguins, leviathans, fishes, and many other creatures feed largely or exclusively on krill. The small invertebrates are interesting as more than just food, however. Accustomed to living in enormous clusters, krill dislike being alone. To ensure this, their eggs are always laid in pairs, and they remain with their hatchmate for life. They are never far from one another, and can be identified by their beating hearts, which are visible through their semitransparent exoskeleton and beat in sync with one another.